QFN Lead Frame Layout Without Connecting Bars for Large Dies
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Solution Overview
Problem
Current Quad Flat No-lead (QFN) packages face inefficiencies in pin layout due to all pins and exposed pads being connected via connecting bars, limiting the layout of power switches when die size is large and the number of pins is high, leading to wasted pins and inefficient utilization.
Innovation Solution
A lead frame design with first and second type pins distributed in central and edge areas respectively, separated without connecting bars, featuring different surface patterns and metals, allowing flexible pin placement and integration of power switches, and a manufacturing method involving selective etching and electroplating to form these pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If all pins and exposed pads are connected via connecting bars to the edge of the package, then the package structure is simplified and manufacturing is easier, but pin layout efficiency deteriorates and power switch placement becomes limited when die size is large
Solution Approach 1:
The patent segments the pins into two distinct types: first type pins distributed in the central area and second type pins distributed in the edge area. This segmentation eliminates the need for connecting bars to link all pins to the edge, as each type can be independently connected to its respective area. The segmentation resolves the contradiction by enabling efficient pin layout for power switches in the central area while maintaining simplified manufacturing for edge-connected pins.
Solution Approach 2:
The patent applies local quality by assigning different connection characteristics to different regions of the lead frame. Central area pins (first type) are optimized for power switch connections without requiring edge connectivity, while edge area pins (second type) maintain traditional edge connections. This localized differentiation allows pin layout efficiency to be improved in the central area without compromising the overall manufacturing simplicity of the package structure.
2Stability of the object's composition
If connecting bars are used to connect all pins to the package edge, then the package structure is more uniform, but pin utilization deteriorates and power switch layout flexibility is reduced
Solution Approach 1:
The patent divides pins into two segments with different connection topologies: first type pins in the central area that do not require connection to the edge, and second type pins in the edge area that maintain traditional edge connections. This segmentation enables adaptable pin placement for power switches in the central area while preserving the uniform structure benefit for edge-connected pins, resolving the contradiction between structural uniformity and placement flexibility.
Solution Approach 2:
The patent transitions from a single-dimension edge-connected pin layout to a two-dimensional distributed pin arrangement. First type pins are distributed across the central area in addition to second type pins at the edge, creating a multi-dimensional connection topology. This dimensional expansion provides flexibility in pin placement while maintaining structural uniformity through systematic distribution patterns.
3Ease of manufacture
If traditional double-surfaces etching and partially electroplating is used, then manufacturing process is simpler, but pin layout optimization for large dies with many pins is limited
Solution Approach 1:
The patent segments the etching and electroplating processes to correspond with the segmented pin types. Different etching patterns and electroplating parameters are applied to central area pins versus edge area pins, enabling precise control over each pin type's geometry and electrical properties while maintaining overall process simplicity through systematic process differentiation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient pin layout and utilization, particularly for large dies, by allowing flexible placement of power switches and reducing pin waste, enhancing the functionality and efficiency of QFN packages.
Implementation Method 1
a manufacturing method involving selective etching and electroplating to form these pins
Implementation Method 2
a manufacturing method involving selective etching and electroplating to form these pins
Data Source
AI summary
A method of forming a lead frame can include: providing a frame base; providing a substrate to support the frame base; and selectively etching the frame base to form first and second type pins. The first type pins are distributed in the central area of the lead frame, and the second type of the pins are distributed in the edge area of the lead frame. The first type pins are separated from the second type of the pins, and the first and second type pins are not connected by connecting bars. A pattern of a first surface of the first and second type pins is different from that of a second surface of the first and second type pins. The metal of the first surface is different from the metal of the second surface, and the second surface is opposite to the first surface.